VGA via SCSI / PowerView - SuperView

[schreinerman]

I had seen PiSCSI is supporting PowerView in a special branch.
see also https://github.com/PiSCSI/piscsi/wiki/PowerView---SuperView

PowerView is a special video graphics card which can be connected via SCSI.

I'm thinking to port it to BlueSCSI v2 and to add:

• SPI TFT
• HDMI Output
• VGA Output

For HDMI / VGA Output this would require some additional PIO and MCU load which is probably not working - but lets see!

Anyhow this would require to add PSRAM and use RP2350B or RP2353B (80-pin variant) because it has more GPIOs than RP2350A (60-pin variant) at the Raspberry Pi Pico 2 (W). There is no evaluation board from the Raspberry Pi Foundation available, so I'm thinking about to make a new design with the chip + PSRAM + official WLAN module of the Raspberry Pi Foundation.
see also

• RP2350: https://www.raspberrypi.com/products/rp2350/
• WLAN Module: https://www.raspberrypi.com/products/radio-module-2/

For a first integration test, I would use RP2350B Plus W from Waveshare to have this additional GPIOs available.
https://www.waveshare.com/rp2350b-plus-w.htm
This would also open some test options for additional PSRAM which is probably required for the graphics video buffer.

[erichelgeson]

That sounds like a fun project! I helped test that feature in PiSCSI - I will note though, SCSI video (even on the real devices) is quite limited and slow. It is a neat feature and really fun to have 2 color screens + the internal screen on a SE/30. To free up enough pio sm you may need to dynamically unload or remove features. As you have questions along the way we're here to help you if you need it (here, discord, email whatever you'd like).

[schreinerman]

Thanks for your offer - as soon I have some hardware in my hands, I will do some tests and will come back to you! I have a PowerBook 170 with no possibility to add any monitor. So it will be an experiment in several directions. So let's see!

[androda]

Here are some thoughts on how this could work, potentially as an Ultra Hat instead of a different RP2350 base board.

BlueSCSI Ultra has a whole lot of GPIO pins exposed on the expansion headers (which I need to make documentation for):

• GPIO 30 through 36 on one header
• GPIO 40 through 47 on another header
  GPIO 37, 38, and 39 are used for I2S with a different height header, so not as useful for making a pcb attach to them.
  The expansion headers include 3.3v sources and ground lines.

What if you were to do synchronized communication between the RP2350B chip on Ultra, and for example a standard RP2350 chip on an Ultra Hat?
The separate RP2350B chip on the Hat can have the PSRAM chip attached (it needs its own flash chip of course).
This would require defining a protocol for sending video data from Ultra to the Hat, so the Hat knows what the resolution is and such. And then the Hat chip can do whatever it wants with the buffered video. Output VGA, DVI, etc.

This would remove the video processing load from Ultra and shift it to a dedicated RP2350 in a Hat, to avoid slowing down the SCSI bus communication and also to avoid running out of DMA channels. There are only one or two DMA channels left after everything which is already going on, and I don't know if that's enough for video output.

And even with all of this happening on the Hat there should still be enough expansion bus pins to connect the RM2 wifi module.

So there you go, an idea that I had this morning while thinking about how the video output system could work.

[schreinerman]

Thanks for your notes / ideas. I will take those into account! Currently I'm waiting for the hardware. As soon everything arrives, I will do some tests. So let's see!